If the grayscale PSD has background transparency and alpha transparency, IM is using the alpha transparency in stead of the background transparency. This is inconsistent with rgb PSD file with both transparency and with grayscale and rgb TIFF files.
Original grayscale PSD:
http://www.fmwconcepts.com/misc_tests/p ... _alpha.psd
Also layers 1 and 2 are coming out cyan rather than gray
convert test3_gray_transback_alpha.psd -separate test3_gray_transback_alpha_%d.png
